1. Field of the Invention
This invention relates to the chemical analysis of substances, and more particularly, to apparatus for supporting and locating a dispensing device in a plurality of stations of a chemical analyzer.
2. State of the Prior Art
A number of automated systems have been developed for performing quantitative chemical analysis of fluid samples. Most of the commercially-available systems utilize liquid reagents and require analyzer equipment having intricate solutions handling and transport capabilities. Recent developments, however, have provided test elements in essentially planar, dry form which can be loaded into a cartridge for use in an analyzer. In the use of such an analyzer, a test element from a cartridge is fed into a metering station where a predetermined amount of sample fluid is deposited on the test element. After an incubation period, a change in the test element is measured at an analysis station, the amount of change being proportional to a particular analyte in the fluid. The test element is used only once and is discarded after the reading has been taken. An analyzer for use with such test elements is disclosed in commonly-assigned U.S. Pat. No. 4,152,390, granted May 1, 1979.
Test elements of the type described above are adapted to function with very small quantities of fluid. For example, test elements for performing colorimetric analyses can produce a measurable response with only ten microliters of sample fluid, and elements for performing potentiometric analyses are operable with ten microliters of sample fluid and ten microliters of reference fluid. Very precise metering devices are required for use with such test elements, since the volume of fluids supplied to the elements should preferably not vary more than five percent (5%) from a selected value to achieve desirable test results. Further, the metering tips through which the fluids are expelled onto the test elements must be precisely located relatively to the elements to obtain accurate test results.
In liquid dispensing systems, it is known to mount a dispensing device on a movable carriage such that the device can be indexed to a plurality of dispensing sites. In the patent to Lenkey, U.S. Pat. No. 3,168,124, granted Feb. 2, 1965, a fluid delivery unit, for dispensing fluids into an array of test tubes, is mounted on a register bar and is advanced past the test tubes by a motor-driven lead screw. Abutments are provided on the register bar and a detent member is adapted to position the dispensing unit at each abutment. Since the apparatus disclosed in the Lenky Patent is used for delivering fluid to a relatively large opening in a test tube, there is no provision for precisely locating the dispensing unit relative to a substrate.
Relatively small, portable analyzers have been developed for use with the generally planar test elements described above. Such analyzers are used in operating rooms for emergency tests, or carried in ambulances for field use. Preferably these analyzers should be simple and manually actuated, since power may not be available. Known metering apparatus for analyzers of this type, however, lack the precision required for acceptable results, and are not suitable for use in multichannel analyzers.